Foamed materials, particularly foamed polyurethane materials, are made by two basic techniques, the frothing method and the blowing method. Blown foams may be assisted in the formation of a cellular structure in the matrix of the foam by the use of nucleating gases. Apparatus and methods for producing foamed materials are shown in U.S. Pat. Nos. 3,286,992; 3,769,232; 3,882,052; 4,264,214; 4,396,529; 4,608,398; 4,778,631; 5,056,034; and 5,264,464. The disclosures of the above patents are expressly incorporated by reference herein.
The present invention relates to an improved apparatus and method for incorporation of additional nucleating sites in a manner which provides a highly uniform microcellular structure in the generated foam. Foams can be produced which are highly uniform and free of weak spots or voids. These foams may be self-adhesive and may not require the presence of additional amine catalysts, auxiliary blowing agents and various modifying reagents, though the use of such materials in the manner known in the art is optional.
These foams may be produced from components which are considerably higher in viscosity than those used in prior processes, thus greatly expanding the range of available raw materials. Polyols and part B components having viscosities of from about 100 centipoise to 35,000 centipoise have been demonstrated. (Brookfield 21/2 rpm, 78.degree. C. or 10,000 centipoise Brookfield 20 rpm, 78.degree. C.) Isocyanates and part A components having viscosities of from about 50 centipoise to 5000 centipoise may be used. It will be appreciated that the practical range of viscosities is limited by the mixing effectiveness of the static mixer. Further, these materials may be reacted without requiring amine catalysts and many of the additive materials, such as blowing agents, required by conventional processes. The resulting product of applicants' method and apparatus has an unexpectedly fine and uniform cellular structure and may be made self-adhering. As a result it can be used as a potting compound in environments where only non-blown materials are currently used, such as filters, since the fine cellular structure is free of the voids and discontinuities which would permit blowbys or otherwise render conventional foams unacceptable.
The isocyanate (part A) and polyol (part B) polyurethane precursors may be those described in U.S. Pat. No. 5,264,464 or equivalent precursors, as is known in the art. However, the apparatus and method as described herein are not restricted to those materials. In particular, materials having a wider viscosity range may be easily used in the apparatus and method disclosed herein. For example, polyols having a viscosity of from 100 to 35,000 centipoise may be used in applicants' process and apparatus. Further, the modifying chemicals, such as surfactants, as described in U.S. Pat. No. 5,264,464 and additives, such as dispersing agents, blowing agents, catalysts, flame retardants and the like, as are known in the art and described in that patent, may be used to produce a suitable foam in the apparatus and method disclosed herein.
Advantageously, the apparatus and method disclosed herein use a static mixer to achieve suitable mixing of the reactant materials. A dynamic mixer is not required to combine the part A and part B reactant chemicals in order to produce a suitable foam. This has a particular advantage on shut-down and cleaning of the apparatus. More specifically, applicants' apparatus and method utilize a static mixer to blend the reactant isocyanate and polyol together and to dispense the polyisocyanate/polyol reactant mixture to form a fine uniform microcellular foam.
The apparatus incorporates a means for introducing a nucleating gas into the polyol (part B) stream, just prior to combining the polyol (part B) and polyisocyanate (part A) reactant streams. This mechanism thoroughly blends the nucleating gas in the part B stream and then introduces it through suitable parallel valving to the static mixer where blending of the part A and part B streams occur. The nucleating gas may be a conventional gas, in particular dry non-reactive gases such as nitrogen or air are preferred. The apparatus also incorporates suitable valving for transferring the reactant streams, parts A and B, from reservoirs in measured quantities, may include additional means for incorporating nucleating gas in the reactant streams and has means for dispensing the polyurethane reaction mixture as a fine microcellular foam. The dispensed foam may be utilized in an industrial process, for example as a self-adhering potting compound.
It is thus an object of the invention to provide an apparatus for producing a uniform microcellular polyurethane foam.
It is a further object of this invention to produce an apparatus for combining polyurethane components A and B in a static mixer to form a foam.
It is a further object of this invention to provide an apparatus for dispensing a fine microcellular uniform polyurethane foam.
It is a further object of this invention to provide an apparatus and method for dispensing a polyurethane reaction mixture to form a fine microcellular foam using a nucleating gas.
It is a further object of this invention to provide a method and apparatus for producing a fine microcellular polyurethane foam in which a nucleating gas is introduced into the polyol (part B) reactant stream prior to combination of the A and B reactant streams.
It is a further object of this invention to produce a self-adhering polyurethane foam.
These and further objects of the invention will be further understood from the Drawings and the Description of the Preferred Embodiments, included herein.